Study of the interrelationship between Legionella pneumophila and free-living amoeba under the condition of natural water temperature to solving legionaires' disease

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It was demonstrated that L. pneumophila shifted into a VNC(Viable but not Culturable) mode inside the Acanthamoeba castellanii cells at a temperature of 15 degrees C by the combination of cultural method, real time PCR(RTPCR) and EMA treated real time PCR(EMA RTPCR), and by transmission electron microscope observation. On the other hand, the shift into VNC state was not observed in Acanthamoeba polyphaga and Haltomannella vermiformis. Culturable L. pneumophila cells were not detected in periodic survey of river water at fixed-sampling points targeting two major rivers in the Tokyo area. A few viable Legionella cells were detected by the combination of RTPCR and EMA RTPCR, however the numbers of viable cells were approximately-same without relation to season. The detection of free-living amoeba(FLA) by PCR showed that the genus Haltomanella was predominant in the sampling points and A. castellanii was not detected. The absence of FLA species that the interrelationship with L. pneumophila is affected by water temperature or few chances to encounter host amoeba by flow of the river might be cause of this result.